01
Length controls more than appearance
For a given headlap, longer slate generally allows greater exposure. Width influences side laps, visual rhythm and piece count. Roof dimensions and course planning may favor particular sizes, but performance requirements should control the selection.
02
Headlap is a system measurement
Headlap describes how far the head of a slate is overlapped by the slate two courses above. Common work often uses 3-inch headlap, but roof pitch, exposure, climate and accepted project details can require different treatment. Do not apply one rule without checking the roof.
03
Pitch changes water behavior
Lower slopes shed water more slowly and can face greater risk from wind-driven rain or ice. Slate systems have slope limitations and detail requirements. Confirm the applicable standard, manufacturer or quarry guidance, and project design before choosing exposure.